The present invention relates generally to fuel consumption measuring devices and more particularly to a method and apparatus for measuring fuel consumption in an internal combustion engine having a fuel injection system.
As a class of internal combustion engines, diesel engines employ a fuel injection system having a pump and a plurality of injectors that meter fuel therefrom to corresponding engine cylinders at various delivery rates depending on such factors as engine load and desired speed. A common characteristic of fuel systems used in diesel engines is the requirement for a fuel return system that collects overflow fuel at each fuel injector of an engine and returns such fuel to the fuel tank for subsequent distribution to the fuel injectors. Such system may comprise a fuel distribution head having an outlet feed line leading to the fuel injectors which include internal fuel return passages communicating with a by-pass line for carrying unburned fuel to the return line and thence to the fuel tank. Additionally, there is a second outlet to return the fuel pump overflow that is delivered to the distribution head. In this form of fuel supply system, approximately two-thirds of the fuel passing through the fuel pump remains in circulation which presents a problem in monitoring actual fuel consumed.
Complexity and expense are coextensive problems that accompany known systems for measuring fuel consumption in diesel engines, mainly because of drastic alterations that have to be made to the fuel piping systems in order to meter and register the difference in flow to the fuel pump and from the return line.
Inaccuracy of readings is another problem that exists for the reason that any system of metering which is subject to the limitations of standard fluid metering techniques and apparatus is prone to the faults and limitations inherent therein. For example, factors which limit the accuracy of known fuel consumption measuring systems include, fluctuations in fuel pressure, fuel temperature, specific gravity, erosion, leaks, blockages, entrained air, and the like. All inhibit the accuracy of such systems to a greater or lesser degree.